diff --git a/spring-boot-project/spring-boot-tools/spring-boot-loader/src/main/java/org/springframework/boot/loader/jar/JarURLConnection.java b/spring-boot-project/spring-boot-tools/spring-boot-loader/src/main/java/org/springframework/boot/loader/jar/JarURLConnection.java
index db34f47c0e..c497346d20 100644
--- a/spring-boot-project/spring-boot-tools/spring-boot-loader/src/main/java/org/springframework/boot/loader/jar/JarURLConnection.java
+++ b/spring-boot-project/spring-boot-tools/spring-boot-loader/src/main/java/org/springframework/boot/loader/jar/JarURLConnection.java
@@ -130,7 +130,7 @@ final class JarURLConnection extends java.net.JarURLConnection {
 			if (spec.endsWith(SEPARATOR)) {
 				spec = spec.substring(0, spec.length() - SEPARATOR.length());
 			}
-			if (spec.indexOf(SEPARATOR) == -1) {
+			if (!spec.contains(SEPARATOR)) {
 				return new URL(spec);
 			}
 			return new URL("jar:" + spec);
diff --git a/spring-boot-project/spring-boot/src/main/java/org/springframework/boot/diagnostics/analyzer/NoUniqueBeanDefinitionFailureAnalyzer.java b/spring-boot-project/spring-boot/src/main/java/org/springframework/boot/diagnostics/analyzer/NoUniqueBeanDefinitionFailureAnalyzer.java
index 7f16a51ff6..50808d2724 100644
--- a/spring-boot-project/spring-boot/src/main/java/org/springframework/boot/diagnostics/analyzer/NoUniqueBeanDefinitionFailureAnalyzer.java
+++ b/spring-boot-project/spring-boot/src/main/java/org/springframework/boot/diagnostics/analyzer/NoUniqueBeanDefinitionFailureAnalyzer.java
@@ -91,7 +91,7 @@ class NoUniqueBeanDefinitionFailureAnalyzer
 	}
 
 	private String[] extractBeanNames(NoUniqueBeanDefinitionException cause) {
-		if (cause.getMessage().indexOf("but found") > -1) {
+		if (cause.getMessage().contains("but found")) {
 			return StringUtils.commaDelimitedListToStringArray(cause.getMessage()
 					.substring(cause.getMessage().lastIndexOf(':') + 1).trim());
 		}
diff --git a/spring-boot-project/spring-boot/src/test/java/org/springframework/boot/context/properties/source/FilteredConfigurationPropertiesSourceTests.java b/spring-boot-project/spring-boot/src/test/java/org/springframework/boot/context/properties/source/FilteredConfigurationPropertiesSourceTests.java
index 8f3d2d4d4b..9bdb10b9c4 100644
--- a/spring-boot-project/spring-boot/src/test/java/org/springframework/boot/context/properties/source/FilteredConfigurationPropertiesSourceTests.java
+++ b/spring-boot-project/spring-boot/src/test/java/org/springframework/boot/context/properties/source/FilteredConfigurationPropertiesSourceTests.java
@@ -114,7 +114,7 @@ public class FilteredConfigurationPropertiesSourceTests {
 	}
 
 	private boolean noBrackets(ConfigurationPropertyName name) {
-		return name.toString().indexOf("[") == -1;
+		return !name.toString().contains("[");
 	}
 
 }
diff --git a/spring-boot-project/spring-boot/src/test/java/org/springframework/boot/context/properties/source/FilteredIterableConfigurationPropertiesSourceTests.java b/spring-boot-project/spring-boot/src/test/java/org/springframework/boot/context/properties/source/FilteredIterableConfigurationPropertiesSourceTests.java
index 7e910f1bfe..fd54f09884 100644
--- a/spring-boot-project/spring-boot/src/test/java/org/springframework/boot/context/properties/source/FilteredIterableConfigurationPropertiesSourceTests.java
+++ b/spring-boot-project/spring-boot/src/test/java/org/springframework/boot/context/properties/source/FilteredIterableConfigurationPropertiesSourceTests.java
@@ -57,7 +57,7 @@ public class FilteredIterableConfigurationPropertiesSourceTests
 	}
 
 	private boolean noBrackets(ConfigurationPropertyName name) {
-		return name.toString().indexOf("[") == -1;
+		return !name.toString().contains("[");
 	}
 
 }